8-07: Diseases of the Inner Ear

1. SENSORINEURAL HEARING LOSS

Diseases of the cochlea and central auditory pathway result in hearing loss, a condition that is usually irreversible. The primary goals in the management of sensory hearing loss are prevention of further losses and functional improvement with auditory rehabilitation, such as with a hearing aid or cochlear implant.

A. Presbycusis

Presbycusis, or age-related hearing loss, is the most frequent cause of sensory hearing loss and is progressive, predominantly high-frequency, and symmetrical. Various etiologic factors (eg, prior noise trauma, drug exposure, genetic predisposition) may contribute to presbycusis. Most patients notice a loss of speech discrimination that is especially pronounced in noisy environments. About 25% of people between the ages of 65 and 75 years and almost 50% of those over 75 experience hearing difficulties. There is emerging evidence that conventional audiometry may not fully capture hearing loss (known as “hidden hearing loss”). Many patients may have subclinical hearing loss. New testing modalities are being devised to detect hearing loss in the setting of normal audiograms.

B. Noise Trauma

Noise trauma is the second most common cause of sensorineural hearing loss. Sounds exceeding 85 dB for 8 hours or more are potentially injurious to the cochlea. The loss typically begins in the high frequencies (especially 4000 Hz) and, with continuing exposure, progresses to involve the speech frequencies. Among the more common sources of injurious noise are industrial machinery, weapons, and excessively loud music. Personal music devices used at excessive loudness levels may also be injurious. Some data suggest that noise cancellation headphones may decrease the need to play music at loud volumes given reduction in background noise. Monitoring noise levels in the workplace by regulatory agencies has led to preventive programs that have reduced the frequency of occupational losses. Individuals of all ages, especially those with existing hearing losses, should wear earplugs when exposed to moderately loud noises and specially designed earmuffs when exposed to explosive noises.